1. Field of the Invention
The present invention relates to a magnetic component for a magnetic length measuring system, a magnetic length measuring system, a length measuring method with a magnetic length measuring system and a production method for a magnetic component for a magnetic length measuring system.
Various methods are known for realizing linear travel measurements. Compared to other methods, magnetically based methods for linear travel measurement have high cross sensitivity with respect to distance changes, temperature changes, and magnetic field strength changes. Therefore, an idea that appears repeatedly is to realize a linear travel measurement using a magnetoresistive angle sensor. Currently there are no cost-effective solution concepts available that satisfy the requirements of accuracy. Furthermore, known stray field-based measuring systems are sensitive to external interference magnetic fields.
An arrangement for measuring a relative linear position is known from EP 0 997 706 B1. The arrangement serves for measuring a relative linear position between a sensor and a magnetic body, with the position relative to each other being linearly adjustable in a predetermined direction. The sensor is embodied as magnetoresistive angle sensor and a magnetic strip is provided as magnetic body. The magnetic strip has a magnetic-pole pair and a magnetic field running at varying angles over the length of said strip; this magnetic field can be visualized by appropriate magnetic field lines. An angle of the magnetic field passing through the magnetoresistive angle sensor is dependent on the relative position of the magnetoresistive angle sensor with respect to the magnetic strip. The respective relative position can be determined from the output signal of the magnetoresistive angle sensor.
Furthermore, DE 199 10 636 A1 discloses a length measuring system that consists of one or more magnetic measuring rods. In at least one measuring rod of the length measuring system the magnetization direction lies in the plane of the cross section thereof, which is perpendicular to the measuring direction, and forms a magnetization pattern. The magnetization of the cross section is homogeneous in a simple case. The magnetization pattern is increasingly twisted with respect to the one at the start of the measuring rod when there is an advance in the measuring direction. The magnetization leads to a magnetic field, the direction of which is likewise continuously rotated with an advance in the measuring direction. The angle of the magnetic field present in the respective position is determined using at least one magnetic field sensor responsive to the direction of the magnetic field, said angle can be uniquely assigned to the position for many different variants of the length measuring system.
The utilized measuring rod is a solid rod magnet with a rotating magnetization. The sensor is situated at a predetermined distance parallel to the longitudinal axis of the rod magnet. The sensor is therefore arranged at such a distance from the rod magnet that it is moved in a region of maximum strength of the magnetic stray field of the rod magnet.
A disadvantage of the arrangements as per the prior art is that it is necessary to realize a magnetization with changing angle along the length of the magnet. The arrangement according to the first example in particular was never implemented because the magnetization cannot be brought about by using known means.
When using a rod magnet, as in DE 199 10 636 A1, it likewise proves impossible to create a continuous, precisely rotating magnetization, particularly at the ends of the rod. The upshot of this is that a measurement using this arrangement is imprecise as a result of the not sufficiently continuously rotated magnetization.
A further disadvantage lies in the fact that the accuracy of the arrangements according to the prior art is dependent on the field homogeneity in the stray field and hence on the distance between the sensor and the magnet. Thus there is an optimum on an axis, lying parallel to the longitudinal axis of the magnet, for the sensor on which a measurement has to be performed. The arrangements as per the prior art accordingly operate using a magnetically inhomogeneous stray field outside of the magnet. As a result of this, the arrangements are very sensitive to external influences, in particular to external interference magnetic fields. This can lead to further imprecision in the measurement.
The field strength moreover also varies as a function of the measuring position. Therefore the rod magnet needs to create correspondingly higher magnetic field strengths for reliable saturation of the sensors.
Furthermore, twisting of the rod magnet as per DE 199 10 636 A1 can over time lead to an accurate measurement no longer being provided. By way of example, the rod magnet can detach from an anchoring over time and rotate along the longitudinal axis thereof. A further disadvantage of the arrangement is that the rod magnet with the rotating magnetization is expensive.